NISTIR 6937 

ENERGY DISSIPATION DEVICES FOR BRIDGES WITH 

STEEL SUPERSTRUCTURES 

Michael A. Riley 

Building and Fire Research Laboratory

Gaithersburg, MD 20899-8611

United States Department of Commerce 

Technology Administration 

National Institute of Standards and Technology

NISTIR 6937 

ENERGY DISSIPATION DEVICES FOR BRIDGES WITH 

STEEL SUPERSTRUCTURES 

Michael A. Riley 

April 2003 

Building and Fire Research Laboratory

National Institute of Standards and Technology

Gaithersburg, MD 20899-8611

United States Department of Commerce 

Donald L. Evans, Secretary

Technology Administration 

Phillip J. Bond, Under Secretary for Technology

National Institute of Standards and Technology

Arden L. Bement, Jr., Director

Energy Dissipation Devices for Bridges with Steel Superstructures

ABSTRACT

Recent earthquakes have clearly demonstrated the seismic vulnerability of bridges constructed

with steel superstructures. The relative flexibility of these bridges, especially in the transverse

direction, may result in overstressing or even failure of components, including trusses, end

diaphragms, beams, bearings, piers, and columns. For the case of slab-on-girder steel bridges,

flexible end diaphragms may experience large deformations, leading to buckling or brittle 

fracture during seismic excitations. However, if the end diaphragms are too stiff, the forces

transmitted through the diaphragms to the bearings and substructure may lead to damage or

failure in the supporting system. Structural dampers and other energy dissipation techniques

are viable options to enhance the ductility and energy dissipation capacity of the diaphragms, 

thereby increasing the safety and reliability of the bridges. Prior research has clearly shown

that ductile end diaphragms can greatly improve the response of steel slab-on-girder bridges;

however, only a limited number of the many available energy dissipation devices have been

investigated. This research effort has focused on analyzing the response of steel slab-on-girder 

bridges that incorporate a wide variety of passive energy dissipation devices in a number of

different configurations. The results of this work show what devices and bracing configurations can best improve the response of slab-on-girder bridges to strong seismic loads. 

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Energy Dissipation Devices for Bridges with Steel Superstructures

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Energy Dissipation Devices for Bridges with Steel Superstructures

ACKNOWLEDGEMENTS

This research was supported by a grant from the Multidisciplinary Center for Earthquake Engineering Research (MCEER) through the MCEER Highway Project, which was funded by the

Federal Highway Administration (FHWA) through contract DTFH61-98-C-00094. The support of MCEER and the FHWA is gratefully appreciated. 

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Energy Dissipation Devices for Bridges with Steel Superstructures

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Energy Dissipation Devices for Bridges with Steel Superstructures

CONTENTS

Abstract ......................................................................................................................... iii

Acknowledgements ...................................................................................................... v

Contents ........................................................................................................................vii

List of Figures ...............................................................................................................ix

1 Introduction............................................................................................................. 1

1.1 Previous Research .................................................................................................................. 1

1.2 Objective of Current Research............................................................................................. 2

2 Bridge Models......................................................................................................... 3

2.1 Scale Model Bridge................................................................................................................ 3

2.2 Numerical Model ................................................................................................................... 4

3 Control Devices and Configurations.................................................................. 7

3.1 Control Devices Considered ................................................................................................ 7

3.1.1 Yielding Metallic Devices.................................................................................................. 7

3.1.2 Friction Devices................................................................................................................. 7

3.1.3 Fluid Viscous Devices........................................................................................................ 8

3.1.4 Viscoelastic Devices........................................................................................................... 8

3.2 Control Device Configurations ........................................................................................... 9

4 Response of Scaled Model Bridge .................................................................... 11

4.1 Response with Viscous Fluid Dampers ........................................................................... 11

4.2 Response with Friction Dampers...................................................................................... 19

4.3 Response with Viscoelastic Dampers .............................................................................. 26

4.4 Response with TADAS Elements ..................................................................................... 32

5 Conclusions ........................................................................................................... 37

6 References.............................................................................................................. 39

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Energy Dissipation Devices for Bridges with Steel Superstructures

viii NIST
Energy Dissipation Devices for Bridges with Steel Superstructures

LIST OF FIGURES

Figure 2.1. Full scale bridge model elevation..................................................................................... 3

Figure 2.2 Full scale bridge model – transverse bracing at abutments........................................... 4

Figure 2.3 Full scale bridge model –general transverse bracing...................................................... 4

Figure 2.4. 2/5 Scale bridge model – transverse bracing at abutments.......................................... 5

Figure 2.5. 2/5 Scale bridge model – general transverse bracing.................................................... 5

Figure 2.6. Three dimensional view of numerical model.................................................................. 6

Figure 3.1 Force displacement loops for friction devices. ................................................................. 7

Figure 3.2 Force-displacement loops for fluid viscous devices. ...................................................... 8

Figure 3.3 Force-displacement loops for viscoelastic devices.......................................................... 9

Figure 3.4. Configuration with dampers inserted into existing cross-braces. ............................. 10

Figure 3.5. Configuration with dampers inserted into chevron cross-braces.............................. 10

Figure 4.1 Deck displacement ratio with viscous fluid dampers in cross braces......................... 11

Figure 4.2 Shear Connector stress ratio with viscous fluid dampers in cross braces. ................. 12

Figure 4.3 Peak forces in viscous fluid dampers in cross braces.................................................... 13

Figure 4.4 Base shear ratio with viscous fluid dampers in cross braces........................................ 13

Figure 4.5 Deck displacement ratio with viscous fluid dampers in chevron braces. .................. 14

Figure 4.6 Shear connector stress ratio with viscous fluid dampers in chevron braces.............. 15

Figure 4.7 Peak forces in viscous fluid dampers in chevron braces............................................... 16

Figure 4.8 Base shear ratio with viscous fluid dampers in chevron braces. ................................. 16

Figure 4.9 Deck displacement ratio with viscous fluid dampers connected to abutments. ....... 17

Figure 4.10 Shear connector stress ratio with VF dampers connected to abutments. ................. 17

Figure 4.11 Peak forces in viscous fluid dampers connected to abutments.................................. 18

Figure 4.12 Base shear ratio with viscous fluid dampers connected to abutments. .................... 18

Figure 4.13 Deck displacement ratio with friction dampers in cross braces................................. 20

Figure 4.14 Shear connector stress ratio with friction dampers in cross braces........................... 20

Figure 4.15 Peak forces in friction dampers in cross braces............................................................ 21

Figure 4.16 Base shear ratio with friction dampers in cross braces................................................ 21

Figure 4.17 Deck displacement ratio with friction dampers in chevron braces. .......................... 22

Figure 4.18 Shear connector stress ratio with friction dampers in chevron braces...................... 22

Figure 4.19 Peak forces in friction dampers in chevron braces....................................................... 23

Figure 4.20 Base shear ratio with friction dampers in chevron braces. ......................................... 23

Figure 4.21 Deck displacement ratio with friction dampers connected to abutments................ 24

Figure 4.22 Shear connector stress ratio with friction dampers connected to abutments. ......... 24

Figure 4.23 Peak forces in friction dampers connected to abutments. .......................................... 25

Figure 4.24 Base shear ratio with friction dampers connected to abutments............................... 25

Figure 4.25 Deck displacement ratio with VE dampers in chevron braces................................... 26

Figure 4.26 Shear connector stress ratio with VE dampers in chevron braces. ............................ 27

Figure 4.27 Base shear ratio with VE dampers in chevron braces.................................................. 27

Figure 4.28 Peak damping forces in VE dampers in chevron braces............................................. 28

Figure 4.29 Peak stiffness forces in VE dampers in chevron braces............................................... 28

Figure 4.30 Deck displacement ratio with VE dampers connected to abutments. ...................... 29

Figure 4.31 Shear connector stress ratio with VE dampers connected to abutments.................. 30

Figure 4.32 Base shear ratio with VE dampers connected to abutments....................................... 30

Figure 4.33 Peak damping forces in VE dampers connected to abutments.................................. 31

Figure 4.34 Peak stiffness forces in VE dampers connected to abutments. .................................. 31

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Energy Dissipation Devices for Bridges with Steel Superstructures

Figure 4.35 Deck displacement ratio with TADAS elements in chevron braces.......................... 33

Figure 4.36 Shear connector stress ratio with TADAS elements in chevron braces. ................... 33

Figure 4.37 Base shear ratio with TADAS elements in chevron braces......................................... 34

Figure 4.38 Peak forces in TADAS elements in chevron braces. .................................................... 34

Figure 4.39 Deck displacement ratio with TADAS elements connected to abutments............... 35

Figure 4.40 Shear connector stress ratio with TADAS elements connected to abutments. ........ 35

Figure 4.41 Base shear ratio with TADAS elements connected to abutments.............................. 36

Figure 4.42 Peak forces in TADAS elements connected to abutments. ......................................... 36

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Energy Dissipation Devices for Bridges with Steel Superstructures

1 INTRODUCTION

Recent earthquakes have clearly demonstrated the seismic vulnerability of bridges

constructed with steel superstructures 

(Housner and Thiel, 1995; Astaneh-Asl et

al., 1994). The relative flexibility of these

bridges, especially in the transverse direction, may result in overstressing or even

failure of components; including trusses,

end-diaphragms, beams, bearings, piers,

and columns. For the case of slab-on-girder

steel bridges, flexible end diaphragms may

experience large deformations leading to

buckling or brittle fracture during seismic

excitations. However, if the end diaphragms are too stiff, the forces transmitted

through the diaphragms to the bearings and

substructure may lead to damage or failure

in the supporting system. 

Seismic isolation is often an effective

method of protecting such bridges from

strong earthquakes. Unfortunately, in 

many cases the cost of retrofitting existing

bridges this way can be quite high, due to 

the need for abutment and pier modifications to allow for the large superstructure 

deflections associated with the isolation devices. 

Innovative techniques such as passive energy dissipation and semi-active devices are 

viable alternative options that enhance the

ductility and energy dissipation capacity of

the diaphragms, thereby increasing the

safety and reliability of steel bridges. Such

devices can be retrofitted into existing steel

bridges, or used in new bridges, either with

or without seismic isolation.

1.1 Previous Research 

Passive energy dissipation devices, commonly known as structural dampers, have

been used in various forms for more than a

quarter of a century. They have mostly

been used to increase the damping of frame

buildings subjected to earthquakes or

strong winds, or to provide additional

damping in seismic isolation systems for

building or bridges. Extensive information

on the development of these devices, theory 

of their operation, and methods for designing structures that incorporate them can be

found in, among other sources, Soong and

Dargush (1997), Hanson and Soong (2001). 

The use of passive energy dissipation devices to improve the response of slab-ongirder highway bridges has only been considered recently. In the aftermath of the

Northridge and Kobe earthquakes, efforts

were undertaken to quantify the effects of

the diaphragms on the seismic response of

these bridges (Zahrai and Bruneau, 1998).

This work showed that only the end diaphragms played a significant role in the lateral response of the bridge. In addition, this

research showed that only a small amount

of stiffness in the end diaphragms was necessary to cause the girders and deck to act

as a rigid unit, while the diaphragms were

intact. However, once the diaphragms

failed large lateral deformations could occur

in the girders, leading to severe damage. 

This finding led to the proposal to use in the

diaphragms and bracing of steel deck-truss

and slab-on-girder bridges ductile members

that employ either yielding metallic dampers or sacrificial shear panels (Sarraf and

Bruneau, 1998a, 1998b; Zahrai and Bruneau,

1999a; 1999b). These authors showed that

such energy dissipation techniques could be

successfully retrofitted into existing highway bridges that do not meet current seismic requirements. Additional research

(Zahrai and Bruneau, 1999b) included experimental testing of three types of ductile

end diaphragms for a slab-on-girder bridge.

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Energy Dissipation Devices for Bridges with Steel Superstructures

Tests were performed on specimens fitted

with diaphragms that utilized eccentrically

braced frames, sacrificial shear panels, and

triangular-plate added damping and stiffness (TADAS) devices. The results of the

tests showed that each of these diaphragm

designs could provide the stiffness and energy dissipation necessary for a retrofitted 

bridge to withstand moderate to large

earthquakes. 

1.2 Objective of Current Research 

The work described above has clearly

shown that ductile end diaphragms can 

greatly improve the response of steel slabon-girder bridges. However, that work has

only scratched the surface with regard to

the available methods of providing energy

dissipation, as it has examined only a limited number of the many possible energy

dissipation devices that are available. 

The research effort reported in this work is

focused on analyzing the response of steel

slab-on-girder bridges that incorporate a

wider variety of passive energy dissipation

devices in a number of different configurations. The objective of this work is to determine which devices and configurations

can best improve the response of these

bridges to extreme seismic loads. 

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Energy Dissipation Devices for Bridges with Steel Superstructures

2 BRIDGE MODELS

All of the bridge models used in this study

were based on the bridge configuration

used by Buckle and Itani in the University

of Nevada, Reno (UNR) study. This bridge

model was, in turn, based on a typical

CALTRANS slab-on-girder highway bridge. 

The model bridge, shown in Figure 2.1

through Figure 2.3, is a three- lane bridge

with four 1.52 m (5 ft) deep girders spaced 

3.35 m (11 ft) on center. The girders are

constructed of A709 Gr50 steel plate, with

22.2 mm (7/8 in) thick plates used for the

webs and 44.5 mm (1 3⁄4 in) thick by 457 mm

(18 in) wide plates used for the flanges. The

reinforced concrete deck slab is 12.95 m

(42 ft 6 in) wide by 219 mm (8 5/8 in) thick. 

The deck was further thickened through a

series of haunches to a depth of 305 mm

(12 in) above the girders. The concrete in

the deck has an fc’ of 27.6 MPa (4 ksi). 

In the design configuration, the bridge was

laterally braced with cross frames consisting

of single 101.6 mm x 101.6 mm x 15.9 mm

(4 in x 4 in x 5/8 in) angles, as shown in

Figure 2.2. These cross-frames were attached to 19.1 mm (3/4 in) thick web stiffeners. To transfer the lateral loads to the

cross-frames equally, 101.6 mm x 101.6 mm

x 15.9 mm (4 in x 4 in x 5/8 in) double angle

struts were used to connect the tops and

bottoms of the web stiffeners. An exception 

was made at the abutment ends of the

bridge, where 267 mm x 452 N/m (WT10.5

x 31) top struts were used in place of the

double angles; these struts were not used to

provide additional lateral stiffness, but instead to transfer impact loads, caused by

traffic passing onto the bridge, more directly from the deck to the girders. 

In its design configuration, the bridge had

four spans supported on abutments at either end and on three 9.75 m (32 ft) high

piers. The end spans were each 40.4 m

(132 ft 6 in) long, while the center spans

were each at 48.8 m (160 ft) long. The piers 

were single column bents with 1.83 m (6 ft)

diameter columns and 2.13 m (7 ft) wide by

1.83 m (6 ft) high pier caps. The lateral

braces were located at the abutments and

piers, and at 4.57 m (15 ft) and 10.7 m (35 ft)

on either side of the piers and abutments.

2.1 Scale Model Bridge 

The primary model used for numerical

simulations was based on the 2/5-scale

model bridge used for experimental testing

at the University of Reno-Nevada. This

bridge model is a single span, two girder

scaled version of the full-scale model, as

shown in Figures 2.4 and 2.5. 

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40.39 m [132'-6"]

2.13 m [7'] 1.83 m [6']

48.77 m [160'] 48.77 m [160'] 40.39 m [132'-6"]

7.92 m [26']

1.83 m [6']

Figure 2.1 Full scale bridge model elevation.
Energy Dissipation Devices for Bridges with Steel Superstructures

The scale model is 18.3 m (60 ft) long, with

two 610 mm (2 ft) deep girders. The girders 

are constructed with 9.53 mm (3/8 in) thick

plates used for the webs and 19.1 mm

(3/4 in) thick by 184 mm (7.25 in) wide

plates used for the flanges. The girders are

centered 1.34 m (4 ft 4 3⁄4 in) apart laterally. 

The reinforced concrete deck is 2.50 m

(8 ft 2 1⁄2 in) wide and 88.9 mm (3 1⁄2 in)

thick. 

The bridge is laterally braced every 3.05 m

(10 ft) with cross frames consisting of a single 50.8 mm x 50.8 mm x 6.35 mm (2 in x

2 in x 1/4 in) angles, with 50.8 mm x

50.8 mm x 6.35 mm (2 in x 2 in x 1/4 in)

double angles providing additional lateral

stiffness at the tops and bottoms of the lateral diaphragms. These struts were connected to 9.53 mm (3/8 in) thick web stiffeners. In a similar manner to the full-scale

bridge, for the end frames 102 mm x

73 N/m (WT4 x 5) top struts were used in

place of the double angles. 

2.2 Numerical Model 

A numerical model of the bridge was developed using the computer program

“SAP2000 Nonlinear”. The deck of the

bridge was modeled using thick shell elements and the main beams were modeled

with thin shell elements, which allowed the

local stresses in the steel sections to be considered. Short shear elements were used to 

model the shear keys in the bridge and allow for the composite action between the

deck and the beams. The braces in the diaphragms were modeled with frame elements, while the isolators and control devices were modeled using the appropriate

3.35 m [11'] 3.35 m [11'] 3.35 m [11']

12.95 m [42'-6"]

Reinforced concrete deck

WT 10.5 x 31

L 4 x 4 x 5/8

2 L 4 x 4 x 5/8 Bearing

219 mm [8 5/8"]

86 mm [3 3/8"]

44 mm [1 3/4"]

1435 mm [4'-8 1/2"]

44 mm [1 3/4"]

Figure 2.2 Full scale bridge model – transverse bracing at abutments. 

12.95 m [42'-6"]

3.35 m [11']

44 mm [1 3/4"]

86 mm [3 3/8"]

1435 mm [4'-8 1/2"]

L 4 x 4 x 5/8

44 mm [1 3/4"]

3.35 m [11']

2 L 4 x 4 x 5/8 Bearing

2 L 4 x 4 x 5/8

219 mm [8 5/8"]

3.35 m [11']

Reinforced concrete deck

Figure 2.3 Full scale bridge model –general transverse bracing. 

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Energy Dissipation Devices for Bridges with Steel Superstructures

nonlinear elements. An image of the model

showing the shell elements and joints can be

seen in Figure 2.6. 

The size of the shell elements were chosen

so that their shape factors were reasonable

and would not adversely impact the simulations, but they were made as large as reasonable to minimize the required computation time. 

2.50 m [8'-2 1/2"]

1.34 m [4'-4 3/4"]

35 mm [1 3/8"]

89 mm [3 1/2"]

572 mm [1'-10 1/2"]

19 mm [3/4"]

19 mm [3/4"]

Bearing

Reinforced concrete deck

WT 4 x 5

L 2 x 2 x 1/4

2 L 2 x 2 x 1/4

Figure 2.4 2/5 Scale bridge model – transverse bracing at abutments. 

1.34 m [4'-4 3/4"]

2.50 m [8'-2 1/2"]

Reinforced concrete deck

2 L 2 x 2 x 1/4

L 2 x 2 x 1/4

2 L 2 x 2 x 1/4

Bearing

89 mm [3 1/2"]

35 mm [1 3/8"]

19 mm [3/4"]

572 mm [1'-10 1/2"]

19 mm [3/4"]

Figure 2.5 2/5 Scale bridge model – general transverse bracing. 

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Energy Dissipation Devices for Bridges with Steel Superstructures

Figure 2.6 Three dimensional view of numerical model. 

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Energy Dissipation Devices for Bridges with Steel Superstructures

3 CONTROL DEVICES AND CONFIGURATIONS

Four types of structural dampers were considered in this investigation. Yielding plate

dampers (TADAS) elements were used in a

configuration similar to that used by Zahrai

and Bruneau (1999b). In addition, these devices were used in a configuration where

devices were connected between the tops of

the bridge beams and the bridge piers or

abutments. Sliding friction dampers, viscoelastic dampers, and viscous fluid dampers were all used to replace the diagonal

braces in the end frames of the bridge, and

to connect the tops of the beams to the

bridge piers or abutments. 

Details of the devices and brace configurations that were used follow. 

3.1 Control Devices Considered 

3.1.1 Yielding Metallic Devices 

Metallic yielding devices take advantage of

the stable hysteretic force-displacement behavior of metals to absorb energy in structures. These devices have taken many

forms, which use flexural, shear, or extensional deformations in the plastic range to

provide the structure with increased stiffness and energy dissipation capacity. Yielding devices have most often been used in 

the bracing systems of building frames or to 

provide additional damping for seismic isolators for both buildings and bridges. 

In this work, triangular added damping and

stiffness (TADAS) devices were chosen.

These devices consist of a number of thin

triangular plates, with their bases rigidly

anchored and their tips connected to a strut

such that they are deformed in bending by

the deflections of the structure. The individual plates are designed so that they will

yield over their entire length when the yield

stress is reached. Thus these devices exhibit

linear stiffness until they yield, after which

they exhibit a force-displacement behavior

that can be approximated by a bilinear

model. 

Their response can be characterized by the

size and number of the triangular plates,

and by the material properties, as described

in the work of Tsai, et al (1993). 

3.1.2 Friction Devices 

Friction devices employ the friction forces

between metal surfaces. These forces can be

modeled as simple Coulomb friction, so the

force-displacement curves of the device, as

shown in Figure 3.1, are rectangular hysteresis loops. The damping mechanism can 

be a friction joint located at the intersection

of cross braces in frames; a device that is

attached to the bracing system and utilizes

friction between metal surfaces, friction

pads, or wedges; or a device that allows slip

to take place in slotted connections. The

devices can be characterized by their slipdisplacement and slip-load. 

For design purposes, the slip-load can be

Displacement

Force

Figure 3.1 Force displacement loops for 

friction devices. 

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Energy Dissipation Devices for Bridges with Steel Superstructures

chosen based on the expected forces and

displacements in the structure. By adjusting

the clamping force on the sliding surfaces of

the device a wide range of slip forces can be

achieved. The slip displacement can be controlled by adjusting the stiffness of the mounting braces. The energy dissipated by the

device during one cycle of motion, , is

equal to the area of the force displacement

curve. The energy that will be dissipated

during a design event, for which the design 

displacement of the devices are known, can 

be set by adjusting the slip force. 

ED

3.1.3 Fluid Viscous Devices

Fluid viscous devices are used in a variety

of structures and mechanical systems to reduce vibrations and impact loads. The devices are typically attached to the bracing

system in buildings. They utilize the dissipation that occurs in fluid flow through orifices, and their cyclic response is a function

of the relative velocity between the ends of

the damper. The devices generally generate

only damping forces, but they may exhibit

some stiffness at high frequencies. 

For the case of a linear device that does not

exhibit stiffness in the high frequency range,

the damping force can be expressed as simply: 

 (3.1) F C

where is the damping coefficient and 

is the stroke velocity. The curve formed by

this idealized force-displacement response

is shown in Figure 3.2. These devices can be

designed to have a wide variety of damping

coefficients and stroke lengths. 

C 

3.1.4 Viscoelastic Devices 

Viscoelastic damping devices are constructed from constrained layers of acrylic

polymers. They are designed so that relative motion between the ends of the device

is translated into shear deformation in the

polymer layers. When deformed, the viscoelastic materials exhibit combined features of elastic solid and viscous liquid.

These devices commonly are used in the

bracing system of moment resisting frames

as energy dissipators for wind and seismic

excitations. 

The devices can be modeled as a spring and

dashpot in parallel (Kelvin model), with the

force expressed by: 

F K C (3.2)  eff  

Here, and are the stroke and stroke

velocity of the device, C is the damping coefficient, and is the effective stiffness of

the device. The effective stiffness of a device can be computed as:

 

Keff

Displacement

Force

Figure 3.2 Force-displacement loops for fluid

viscous devices. 



0

 F0

 

F

 

K

F F

eff 



 

  (3.3) 

Here, F and F 



 are the forces corresponding to the maximum and minimum

displacements, and  , respectively, as 

8 NIST
Energy Dissipation Devices for Bridges with Steel Superstructures

indicated in Figure 3.3. The damping coefficient of the device can then be expressed

as: 

C

ED

ave

 2 (3.4)

Here, is the dissipated energy, which is

equal to the area enclosed by one complete

cycle of the force-displacement response, 

is the angular frequency, and  is the

average of the magnitudes of and . 

The effective stiffness and the damping coefficient of a viscoelastic device are generally dependent on the excitation frequency

and the operating temperature, including

the temperature rise due to excitation. 

ED

ave

 

3.2 Control Device Configurations 

Three device configurations were used in

this study. The first configuration, shown

in Figure 3.4, used devices inserted into the

existing cross braces of the end diaphragms.

This configuration is practical for many

types of structural dampers, but not for all.

In particular, the TADAS dampers cannot

be easily used in this configuration.

The second configuration, shown in Figure

3.5, used chevron braces with the damper

located between the diagonal braces and the

bottom strut of the diaphragm. This is the

configuration used with the TADAS elements and ductile shear panels in previous

research (Zahrai and Bruneau, 1999b). 

The third configuration was similar to the

previous one, except that a strut was used 

to connect the damping element directly to

the bridge abutment, instead of the bottom

strut of the diaphragm. This configuration

has the advantage of including both lateral

the deformations in the end diaphragm and

the deformations in the bridge bearings in

the motion that activates the damper. 

Displacement

Forc

e

Keff

 





Figure 3.3 Force-displacement loops for viscoelastic devices. 

F

F

1

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Energy Dissipation Devices for Bridges with Steel Superstructures

10 NIST

Figure 3.4 Configuration with dampers inserted into existing cross-braces. 

Figure 3.5 Configuration with dampers inserted into chevron cross-braces. 
Energy Dissipation Devices for Bridges with Steel Superstructures

4 RESPONSE OF SCALED MODEL BRIDGE

4.1 Response with Viscous Fluid

Dampers 

The viscous fluid dampers were used in all

three of the device configurations, and performed well in each case. Each configuration was simulated for a range of damper 

sizes, with damping coefficients ranging

from 0.007 kN/mm·s (0.04 kip/in·s) to

17.5 kN/mm·s (100 kip/in·s). 

In the cross-brace configuration these

dampers were able to significantly improve

the response of the bridge superstructure;

however, they were able to provide only a

marginal decrease in the forces transferred

from the superstructure to the abutments. 

Figure 4.1 shows the ratio between the displacement of the deck of the controlled

bridge and that of the bridge with conventional diaphragms. For the cases with relatively small dampers, the deck displacements increased significantly — by as much

as 80%. These increases are due to the stiffness of the structure being greatly decreased, while the dampers do not remove

enough energy to compensate for the loss of

stiffness. When properly sized dampers

were used, the damping forces more than

compensated for the stiffness reduction, and

the peak displacements were reduced by as

much as 80%. The mean reduction with the

larger dampers was more that 60%. 

Even better response improvements occurred with the shear forces between the

deck and the girders. Figure 4.2 shows the

ratios of the shear stresses in the end shear

connectors —those closest to the abutments.

Only in the cases of the smallest dampers

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0.01 0.1 1 10

Damper Coefficient (kN/mm·s)

Displace

ment Ratio

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Mean Ratio

Figure 4.1 Deck displacement ratio with viscous fluid dampers in cross braces. 

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Energy Dissipation Devices for Bridges with Steel Superstructures

was there any increase in the shear, while

the largest dampers were able to reduce the

shears by 90%. These reductions are due to

a combination of the energy dissipation in

the dampers and the softer response of the

less stiff superstructure. The damping

forces required to achieve these improvements are shown in Figure 4.3. 

Unfortunately, the viscous fluid dampers in

the cross-brace configuration could not provide significant reductions in the forces in

the bridge bearings and abutments. Figure

4.4 shows the ratio of base shear forces in

the bearings at one end of the bridge. As

was the case for the shear stress in the shear 

connectors, there were small increases in the

base shear when the dampers were small.

Increasing the size of the dampers did not

lead to large decreases in the base shear.

For the largest dampers, the base shear was

reduced by only about 15%, and for the case

of the Pacoima Dam earthquake record

there was almost no response reduction. 

In the chevron brace configuration the viscous fluid dampers performed slightly

worse than in the cross brace configuration,

and again they did not significantly reduce

the forces transferred to the substructure. 

The ratio between the deck displacements

in the bridges with controlled and conventional diaphragms is shown in Figure 4.5.

Again, the reduction in the diaphragm stiffness led to increases in the displacements

when the damper were small, but the larger

dampers were able to reduce the peak displacements by an average of nearly 60%. 

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.01 0.1 1 10

Damper Coefficient (kN/mm·s)

Shear Rati

o

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Mean Ratio

Figure 4.2 Shear Connector stress ratio with viscous fluid dampers in cross braces. 

12 NIST
Energy Dissipation Devices for Bridges with Steel Superstructures

0

10

20

30

40

50

60

0.01 0.1 1 10

Damper Coefficient (kN/mm·s)

Force (k

N)

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Figure 4.3 Peak forces in viscous fluid dampers in cross braces. 

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

0.01 0.1 1 10

Damper Coefficient (kN/mm·s)

Base Shear Rati

o

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Mean Ratio

Figure 4.4 Base shear ratio with viscous fluid dampers in cross braces. 

NIST 13
Energy Dissipation Devices for Bridges with Steel Superstructures

The shear forces between the deck and the

girders were reduced in nearly all of the

cases. Figure 4.6 shows the connector stress

ratios between the controlled and conventional cases. Here, the mean reduction during the five earthquake excitations was as

great as 80%. The damper forces required

to achieve these response improvements are

shown in Figure 4.7 

As in the case with the dampers in the 

cross-bracing, the viscous dampers in the

chevron-braced configuration had only a

limited effect on the shear forces between

the girders and abutments. As can be seen

in Figure 4.8, the smallest dampers allowed

the base shears to increase, while the largest

dampers reduced the base shears by an average of 10%. 

The third configuration that was considered

for the viscous fluid dampers consisted of

the dampers connected between the abutments and braces connected to the tops of

the girder web stiffeners. This configuration performed poorly compared to the 

other two. 

The displacement responses for this configuration are shown in Figure 4.9. The response with the smallest dampers was similar to the response with the smallest dampers in the chevron brace configuration, but

the average improvement with the largest

dampers was only about 50%. 

In this configuration, even the smallest

dampers were able to reduce the peak shear

stresses between the girders and the deck

by an average of 10%; however, the mean

reduction due to the largest dampers was

only about 60%. This is, of course, an impressive improvement in the structural response, but it is small in comparison to the

improvements achieved by the cross-braced

and chevron-braced configurations. 

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0.01 0.1 1 10 100

Damper Coefficient (kN/mm·s)

Displacement Rati

o

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Mean Ratio

Figure 4.5 Deck displacement ratio with viscous fluid dampers in chevron braces. 

14 NIST
Energy Dissipation Devices for Bridges with Steel Superstructures

In all three brace configurations, the viscous

fluid dampers were able to significantly

improve the response of the superstructure, 

with the cross-brace configuration providing the best improvements. The configuration that connects the dampers directly to

the abutments has good potential for cases

where the substructure has adequate reserve strength, but where the bearing

strength is limited. Unfortunately, none of

these configurations are appropriate when

the substructure is inadequate for the seismic loads. 

The peak damper forces are shown in

Figure 4.11. These forces are significant because in this configuration they are being

transmitted directly to the abutments.

Figure 4.12 shows the ratios between the

peak base shear forces of the damped and

conventional diaphragm cases. In this configuration, best improvements in the base

shear response occur with the medium

sized dampers. The increased base shears

that occur with the large dampers are directly due to the large damping forces. In

fact, the forces transmitted through the

bridge bearings are significantly reduced by

the largest dampers in this configuration. 

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.01 0.1 1 10 100

Damper Coefficient (kN/mm·s)

Shear Rati

o

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Mean Ratio

Figure 4.6 Shear connector stress ratio with viscous fluid dampers in chevron braces. 

NIST 15
Energy Dissipation Devices for Bridges with Steel Superstructures

0

10

20

30

40

50

60

70

80

90

100

0.01 0.1 1 10 100

Damper Coefficient (kN/mm·s)

Force (kN)

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Figure 4.7 Peak forces in viscous fluid dampers in chevron braces. 

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

0.01 0.1 1 10 100

Damper Coefficient (kN/mm·s)

Base Shear Rati

o

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Mean Ratio

Figure 4.8 Base shear ratio with viscous fluid dampers in chevron braces. 

16 NIST
Energy Dissipation Devices for Bridges with Steel Superstructures

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0.01 0.1 1 10

Damper Coefficient (kN/mm·s)

Displacement Ratio

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Mean Ratio

Figure 4.9 Deck displacement ratio with viscous fluid dampers connected to abutments. 

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.01 0.1 1 10

Damper Coefficient (kN/mm·s)

Shear Rati

o

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Mean Ratio

Figure 4.10 Shear connector stress ratio with VF dampers connected to abutments. 

NIST 17
Energy Dissipation Devices for Bridges with Steel Superstructures

0

10

20

30

40

50

60

0.01 0.1 1 10

Damper Coefficient (kN/mm·s)

Force (kN)

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Figure 4.11 Peak forces in viscous fluid dampers connected to abutments.

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

0.01 0.1 1 10

Damper Coefficient (kN/mm·s)

Base Shear Rati

o

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Mean Ratio

Figure 4.12 Base shear ratio with viscous fluid dampers connected to abutments.

18 NIST
Energy Dissipation Devices for Bridges with Steel Superstructures

4.2 Response with Friction Dampers 

Friction dampers were used in all three

brace configurations and performed acceptably in each. However, these dampers

tended to perform poorly as compared to

the viscous fluid dampers. The response

was simulated for dampers with slip forces

ranging from 0.445 kN (0.1 kip) to 445 kN

(100 kip). 

The response with the friction dampers in

the cross-brace configuration is shown in

Figure 4.13 through Figure 4.16. While the

smallest dampers performed poorly, allowing the displacements and shear forces to

increase, the medium sized dampers were

able to significantly improve the response of

the bridge. As the dampers became larger,

the response forces were not large enough 

to activate the dampers, and the bridge responses approached those of the bridge

with conventional diaphragms. 

The best responses occurred for dampers

with slip forces of 30 kN to 45 kN, representing 40% to 60% of the tributary weight

of the superstructure. With these dampers,

the average of the peak deck displacements

was reduced by more than 30% and the average of the peak shear forces between the

deck and girders was reduced by more than

40%. However, the base shear was only reduced about 5%. 

The response with the friction dampers in

the chevron-brace configuration was similar

to the response in the cross-brace configuration. As can be seen in Figure 4.17 through

Figure 4.20, the smallest dampers had little

impact on the response, while the largest

ones were not activated and instead acted

as rigid struts. 

The dampers with slip forces between

20 kN and 45 kN performed best, with a slip

force equal to about 35% of the tributary

weight appearing to be optimal for this configuration. In this case, the displacements

were reduced by an average of 15% and the

shear between the deck and the girders by

about 25%. This configuration had no impact on the base shear forces. 

The final configuration for the friction

dampers was with the dampers connected

directly to the bridge abutments. The response with this configuration, shown in 

Figure 4.21 through Figure 4.24, tended to 

be somewhat better than the response with

either the cross brace or chevron brace configurations. 

In this configuration, the best damper slip

force varied with the response of interest.

The displacements were reduced the most 

with damper slip forces between 45 kN and

70 kN. These dampers reduced the average

response by about 50%. The shear forces

between the deck and girders were reduced 

the most by dampers with slip forces between 30 kN and 45 kN. In these cases the

response was reduced by more than 40%.

The average of the peak base shears was

reduced by 20% by dampers with slip forces

between 10 kN and 20 kN. Larger dampers

significantly increased the base shear forces.

As in the case of the viscous fluid dampers,

the friction dampers were able to improve 

the response of the superstructure in all

three brace configurations. However, the

response improvements tended to be

smaller than with the fluid dampers. The 

major advantage to using friction devices

instead of the fluid dampers would be the

cost of the devices, which could make the

friction devices more practical for many retrofit situations. 

NIST 19
Energy Dissipation Devices for Bridges with Steel Superstructures

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

1 10 100 1000

Friction Force (kN)

Displacement R

atio

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Mean Ratio

Figure 4.13 Deck displacement ratio with friction dampers in cross braces. 

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1 10 100 1000

Friction Force (kN)

Shear Ratio

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Mean Ratio

Figure 4.14 Shear connector stress ratio with friction dampers in cross braces. 

20 NIST
Energy Dissipation Devices for Bridges with Steel Superstructures

0

10

20

30

40

50

60

70

80

90

100

1 10 100 1000

Friction Force (kN)

Force (kN)

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Figure 4.15 Peak forces in friction dampers in cross braces. 

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

1 10 100 1000

Friction Force (kN)

Base Shear Ratio

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Mean Ratio

Figure 4.16 Base shear ratio with friction dampers in cross braces. 

NIST 21
Energy Dissipation Devices for Bridges with Steel Superstructures

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

1 10 100 1000

Friction Force (kN)

Displacement R

atio

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Mean Ratio

Figure 4.17 Deck displacement ratio with friction dampers in chevron braces. 

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1 10 100 1000

Friction Force (kN)

Shear R

atio

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Mean Ratio

Figure 4.18 Shear connector stress ratio with friction dampers in chevron braces. 

22 NIST
Energy Dissipation Devices for Bridges with Steel Superstructures

0

10

20

30

40

50

60

70

80

90

100

1 10 100 1000

Friction Force (kN)

Force (kN)

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Figure 4.19 Peak forces in friction dampers in chevron braces. 

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

1 10 100 1000

Friction Force (kN)

Base Shear R

atio

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Mean Ratio

Figure 4.20 Base shear ratio with friction dampers in chevron braces. 

NIST 23
Energy Dissipation Devices for Bridges with Steel Superstructures

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

1 10 100 1000

Friction Force (kN)

Displacement R

atio

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Mean Ratio

Figure 4.21 Deck displacement ratio with friction dampers connected to abutments. 

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1 10 100 1000

Friction Force (kN)

Shear R

atio

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Mean Ratio

Figure 4.22 Shear connector stress ratio with friction dampers connected to abutments. 

24 NIST
Energy Dissipation Devices for Bridges with Steel Superstructures

0

10

20

30

40

50

60

70

80

90

100

1 10 100 1000

Friction Force (kN)

Force (kN)

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Figure 4.23 Peak forces in friction dampers connected to abutments. 

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

1 10 100 1000

Friction Force (kN)

Base Shear R

atio

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Mean Ratio

Figure 4.24 Base shear ratio with friction dampers connected to abutments. 

NIST 25
Energy Dissipation Devices for Bridges with Steel Superstructures

4.3 Response with Viscoelastic

Dampers 

The viscoelastic (VE) dampers were used in

two brace configurations, the chevron

braces and braces directly connected to the

abutments. These devices performed acceptably in both configurations, but the resulting response was not as good as with

the viscous fluid dampers and was mixed as

compared to the friction dampers. 

A single type of viscoelastic material was

chosen for the simulations. The material

had a shear storage modulus of 965 kPa

(140 psi) and a shear loss modulus of 

1165 kPa (169 psi). This led to a series of

dampers that all had a constant ratio of 8.2

between the damping coefficient and stiffness. Dampers were simulated with damping coefficients ranging from

0.007 kN/mm·s (0.04 kip/in·s) to

17.5 kN/mm·s (100 kip/in·s), and the associated stiffness ranging from 0.058 kN/mm

(0.33 kip/in) to 144 kN/mm (823 kip/in). 

In the chevron brace configuration, the

smallest of these dampers performed similarly to the viscous fluid devices, but as the

size of the VE devices increased, the stiffness component of the device response became significant and these devices improved the response less. The most efficient

dampers, with damping coefficients between 2 kN/mm·s and 3 kN/mm·s, were

able to reduce the deck displacements by an

average of 20%, as shown in Figure 4.25. 

These devices were also able to reduce the

shear forces between the deck and the girders by 30%, as shown in Figure 4.26. 

The VE dampers in this configuration had

little impact on the base shear forces, as

shown in Figure 4.27. The peak damping

and stiffness components of the damper 

forces are shown in Figure 4.28 and Figure

4.29, respectively. 

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0.01 0.1 1 10

Damper Coefficient (kN/mm·s)

Displacement Rati

o

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Mean Ratio

Figure 4.25 Deck displacement ratio with VE dampers in chevron braces. 

26 NIST
Energy Dissipation Devices for Bridges with Steel Superstructures

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.01 0.1 1 10

Damper Coefficient (kN/mm·s)

Shear Rati

o

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Mean Ratio

Figure 4.26 Shear connector stress ratio with VE dampers in chevron braces. 

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

0.01 0.1 1 10

Damper Coefficient (kN/mm·s)

Base Shear Rati

o

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Mean Ratio

Figure 4.27 Base shear ratio with VE dampers in chevron braces. 

NIST 27
Energy Dissipation Devices for Bridges with Steel Superstructures

0

10

20

30

40

50

60

0.01 0.1 1 10

Damper Coefficient (kN/mm·s)

Force (kN)

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Figure 4.28 Peak damping forces in VE dampers in chevron braces. 

0

10

20

30

40

50

60

0.01 0.1 1 10

Damper Coefficient (kN/mm·s)

Force (kN)

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Figure 4.29 Peak stiffness forces in VE dampers in chevron braces. 

28 NIST
Energy Dissipation Devices for Bridges with Steel Superstructures

When the VE dampers were connected directly to the abutments they performed

slightly better and the best response was

provided by smaller dampers. In this configuration, VE dampers with damping coefficients between 0.7 kN/mm·s and

1.1 kN/mm·s were able to reduce the peak

deck displacements by an average of about

25%, as shown in Figure 4.30. Similarly,

devices with damping coefficients between

0.2 kN/mm·s and 0.7 kN/mm·s were able

to reduce the peak shear forces between the

deck and the girders by about 33%. This

response is shown in Figure 4.31. 

The most effective dampers were able the

base shear forces by an average of 20%, as

shown in Figure 4.32. As was the case with

the viscous fluid dampers and friction devices, the minimum base shear occurred just

before the damper forces, shown in Figure

4.33 and Figure 4.34, became the most significant portion of the total base shear.

When the damper forces are excluded from

the base response, the remaining forces,

which are due to the shear in the bearings,

continue to decrease as the damper size increases. 

As in the case of the viscous fluid and friction dampers, the viscoelastic dampers were

able to improve the response of the superstructure in all three brace configurations.

However, like the friction dampers, the response improvements tended to be smaller

than with the fluid dampers. Due to the

viscoelastic material’s temperature dependence and no strongly compelling performance advantage, these devices are judged

not to be practical for use in highway

bridges. 

0.0

0.2

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0.8

1.0

1.2

1.4

1.6

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2.0

0.01 0.1 1 10

Damper Coefficient (kN/mm·s)

Displacement Rati

o

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Mean Ratio

Figure 4.30 Deck displacement ratio with VE dampers connected to abutments.

NIST 29
Energy Dissipation Devices for Bridges with Steel Superstructures

0.0

0.2

0.4

0.6

0.8

1.0

1.2

0.01 0.1 1 10

Damper Coefficient (kN/mm·s)

Shear Rati

o

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Mean Ratio

Figure 4.31 Shear connector stress ratio with VE dampers connected to abutments. 

0.00

0.25

0.50

0.75

1.00

1.25

1.50

1.75

2.00

0.01 0.1 1 10

Damper Coefficient (kN/mm·s)

Base Shear Rati

o

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Mean Ratio

Figure 4.32 Base shear ratio with VE dampers connected to abutments. 

30 NIST
Energy Dissipation Devices for Bridges with Steel Superstructures

0

10

20

30

40

50

60

0.01 0.1 1 10

Damper Coefficient (kN/mm·s)

Force (kN)

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Figure 4.33 Peak damping forces in VE dampers connected to abutments. 

0

10

20

30

40

50

60

0.01 0.1 1 10

Damper Coefficient (kN/mm·s)

Force (kN)

El Centro

Pacoima

Loma Prieta

Northridge

Whittier

Figure 4.34 Peak stiffness forces in VE dampers connected to abutments.

NIST 31
Energy Dissipation Devices for Bridges with Steel Superstructures

4.4 Response with TADAS Elements

The TADAS elements were used in the

same two brace configurations as the viscoelastic devices — the chevron braces and

directly connected to the abutments. These

devices performed acceptably in both configurations. They tended to perform

slightly better than the friction dampers and

viscoelastic dampers, but they did not perform as well as the viscous fluid dampers. 

All of the TADAS elements were assumed

to be constructed from mild steel. By varying the plate thickness, height, and base

width, along with the number of plates

used in a single device, both the elastic

stiffness and the yield force could be adjusted independently over a wide range.

For the model scale bridge, simulations

were performed with TADAS elements having elastic stiffnesses from 11 kN/mm to

332 kN/mm, and with yield forces ranging

from 9 kN to 90 kN. The upper end to the

elastic stiffness was chosen because, even at

the model scale, stiffer devices with the

given range of yield forces were not physically practical. 

The mean responses of the model scale

bridge with TADAS elements in chevron

braces, subjected to the five earthquake records, are shown in Figure 4.35 through

Figure 4.38. The TADAS elements with the

smallest elastic stiffnesses had little impact

on the response of the bridge; however, as

the device stiffness became larger, the devices with yield forces between 35 kN and

55 kN were able to reduce the deck displacements by more than 30% and the shear

between the deck and the girders by more 

than 35%. These forces correspond to 45% 

to 70% of the tributary weight of the bridge. 

The TADAS elements in this configuration

had little impact on the shear forces between the superstructure and the abutments. The stiffest dampers reduced this

response by only about four percent. 

When the TADAS elements were connected

directly to the bridge abutments, they further reduced the superstructure response at 

the expense of significantly increased base

shears. As can be seen in Figure 4.39, the

peak deck displacements were reduced by

as much as 50%, while the peak shear forces

between the deck and the girders, shown in

Figure 4.40, were reduced by 40%. 

Unfortunately, in this configuration the

damper forces, shown in Figure 4.42, directly contributed to the forces transmitted

to the abutments. As can be seen in Figure

4.41, these forces were always larger for the

cases with the TADAS elements than for the

bridge with a conventional diaphragm, and

for the cases of the stiff dampers with large

yield forces the base shears were greatly

increased. 

32 NIST
Energy Dissipation Devices for Bridges with Steel Superstructures

11 19

33

59

105

187

332

8.9

14.2

22.2

35.6

56.0

89.0

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Displacement Ratio

Damper Stiffness (kN/mm) Yield Force (kN)

Figure 4.35 Deck displacement ratio with TADAS elements in chevron braces. 

11 19

33

59

105

187

332

8.9

14.2

22.2

35.6

56.0

89.0

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Shear Ratio

Damper Stiffness (kN/mm) Yield Force (kN)

Figure 4.36 Shear connector stress ratio with TADAS elements in chevron braces. 

NIST 33
Energy Dissipation Devices for Bridges with Steel Superstructures

11 19

33

59

105

187

332

8.9

14.2

22.2

35.6

56.0

89.0

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Base Shear Ratio

Damper Stiffness (kN/mm) Yield Force (kN)

Figure 4.37 Base shear ratio with TADAS elements in chevron braces. 

11 19

33

59

105

187

332

8.9

14.2

22.2

35.6

56.0

89.0

0.0

10.0

20.0

30.0

40.0

50.0

60.0

Force (kN)

Damper Stiffness (kN/mm) Yield Force (kN)

Figure 4.38 Peak forces in TADAS elements in chevron braces. 

34 NIST
Energy Dissipation Devices for Bridges with Steel Superstructures

11

19

33

59

105

187

332

8.9

14.2

22.2

35.6

56.0

89.0

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Displacement Ratio

Damper Stiffness (kN/mm) Yield Force (kN)

Figure 4.39 Deck displacement ratio with TADAS elements connected to abutments. 

11

19

33

59

105

187

332

8.9

14.2

22.2

35.6

56.0

89.0

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Shear Ratio

Damper Stiffness (kN/mm) Yield Force (kN)

Figure 4.40 Shear connector stress ratio with TADAS elements connected to abutments. 

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Energy Dissipation Devices for Bridges with Steel Superstructures

11 19

33

59

105

187

332

8.9

14.2

22.2

35.6

56.0

89.0

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

Base Shear Ratio

Damper Stiffness (kN/mm) Yield Force (kN)

Figure 4.41 Base shear ratio with TADAS elements connected to abutments. 

11

19

33

59

105

187

332

8.9

14.2

22.2

35.6

56.0

89.0

0.0

10.0

20.0

30.0

40.0

50.0

60.0

Force (kN)

Damper Stiffness (kN/mm) Yield Force (kN)

Figure 4.42 Peak forces in TADAS elements connected to abutments. 

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Energy Dissipation Devices for Bridges with Steel Superstructures

5 CONCLUSIONS

The results of the analyses summarized in

this report show that energy dissipation devices located in ductile end diaphragms can 

significantly reduce the response of slab-ongirder bridges subjected to strong seismic

excitation. All the devices and brace configurations that were considered were able

to improve the response of the superstructure, although some devices and configurations were more effective than others. Unfortunately, only small reductions were obtained in the forces transmitted from the

bridge to the substructure. 

The viscous fluid dampers were able to 

greatly improve the response of the superstructure in all the brace configurations.

These devices have the advantage of not

having any inherent stiffness. When the

dampers are properly sized for the application, the energy dissipation they provide

more than compensates for the reduced

stiffness. The latter tends to reduce the 

forces and stresses at the expense of the lateral displacements, and results in both reduced displacement response and reduced

forces in the superstructure. 

The friction dampers, viscoelastic dampers,

and TADAS elements all improved the response of the superstructure when they

were properly sized; however, the response

improvements tended to be smaller than

with the viscous fluid dampers. The choice

of one of these devices for a particular application will be based more on cost and

maintenance issues, as well as on temperature dependence, rather than on effectiveness alone. 

Considering the cost and maintenance issues may change how the response results

are interpreted. In particular, the viscous

fluid dampers are potentially the most expensive of the devices considered in this

report. Their superior response improvement makes them good candidates when

potentially less expensive options cannot

provide the necessary response reductions.

The friction dampers and TADAS elements

are relatively inexpensive by comparison,

and may be preferable when lesser response

reductions are necessary. Viscoelastic

dampers are temperature sensitive, which

when combined with their merely average

response improvements, makes them an 

unlikely candidate for highway bridge applications. 

All three brace configurations performed

well, with no one configuration consistently

performing better than the other two. The

selection of a brace configuration is thus

likely to be based on the practicality of using that configuration with the chosen energy dissipation system for a specific

bridge. 

The cross brace configuration, while simple

in theory, may not always be practical in

application. The lateral offset necessary to

allow the braces to cross has the potential to

create eccentric forces when used with large

dampers, which can increase stresses at the

connectors and may cause buckling of the

struts. 

The chevron brace configuration will generally be practical, but it may require significant strengthening of either the top or bottom struts in the diaphragm. The configuration that connects the dampers directly to

the abutments has good potential for cases

where the substructure has adequate reserve strength, but where the bearing

strength is limited. Unfortunately, none of

the configurations is appropriate when the

substructure is inadequate for the seismic

loads. 

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38 NIST
Energy Dissipation Devices for Bridges with Steel Superstructures

6 REFERENCES

Astaneh-Asl, A., Bolt, B., McMullin, K.,

Modjtahedi, D., Cho, S., and Donikian,

R. (1194). “Seismic performance of steel

bridges during the 1994 Northridge

Earthquake.” Report Number UCB/CESteel-94/01, Dept. of Civil Engineering,

University of California, Berkeley, Calif. 

Hanson, R. D., and Soong, T. T. (2001).

“Seismic Design with Supplemental Energy Dissipation Devices”, EERI Monograph MNO-8, EERI, Oakland, CA. 

Housner, G., and Thiel, C. (1995). “The continuing challenge: Report on the performance of state bridges in the Northridge Earthquake.” Earthquake Spectra, 

11(4), 607-636. 

Sarraf, M. and Bruneau, M. (1998a). “Ductile Seismic Retrofit of Steel Deck-Truss

Bridges. I: Strategy and Modeling”,

Journal of Structural Engineering, ASCE,

124(11), pp. 1253-1262. 

Sarraf, M. and Bruneau, M. (1998b). “Ductile Seismic Retrofit of Steel Deck-Truss

Bridges. II: Design Applications”, Journal of Structural Engineering, ASCE,

124(11), pp. 1263-1271. 

Soong, T. T., and Dargush, G. F. (1997). Passive Energy Dissipation Systems in Structural Engineering, John Wiley& Sons, 

New York, NY. 

Tsai, K. C., Chen, H. W., Hong, C. P., and

Su, F. Y. (1993). “Design of Steel Triangular Plate Energy Absorbers for Seismic-resistant Construction”, Earthquake

Spectra, 9(3), 505-528. 

Zahrai, S. M. and Bruneau, M. (1998). “Impact of Diaphragms on the Seismic Response of Straight Slab-On-Girder Steel

Bridges”, Journal of Structural Engineering, ASCE, 124(8), pp. 938-947. 

Zahrai, S. M. and Bruneau, M. (1999a).

“Ductile End Diaphragms for Seismic

Retrofit of Slab-On-Girder Steel

Bridges”, Journal of Structural Engineering, ASCE, 125(1), pp. 71-80. 

Zahrai, S. M. and Bruneau, M. (1999b).

“Cyclic Testing of Ductile End Diaphragms for Slab-On-Girder Steel 

Bridges”, Journal of Structural Engineering, ASCE, 125(9), pp. 987-996. 

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